Magnesium isotopes in permafrost-dominated Central Siberian larch forest watersheds

The Mg isotopic compositions of Larix gmelinii organs (i.e., stem wood, roots and needles) exhibit a low variability. However, an enrichment of 0.2-0.3‰ in the δ26Mg of larch needles in the course of the growing season, from June to September can be observed. This enrichment most likely demonstrates uptake of isotopically heavier Mg by the plant in addition to the progressive thawing of the mineral soil (deepening of the active layer of the soil). Overall, the Mg isotope approach indicates the important contribution of vegetation (larch needles, mosses and dwarf shrubs) to the riverine Mg isotope signature and helps to reveal the contribution of isotopically light carbonate rocks in the large rivers of the Central Siberian Plateau.